1. Field of the Invention
The present invention relates to a semiconductor device having both an image sensor function and a picture display function. More particularly, the present invention relates to an active matrix type semiconductor device constituted by a plurality of thin film transistors (TFTs) arranged in a matrix form.
2. Description of the Related Art
In recent years, a technique for a TFT using polycrystal silicon (polysilicon TFT) has been diligently studied. As a result, it becomes possible to form a driver circuit including a shift register circuit and the like by use of the polysilicon TFT, and an active matrix type liquid crystal panel in which a pixel region and a peripheral driver circuit for driving the pixel region are integrated on the same substrate has been put to practical use. Thus, a liquid crystal panel is miniaturized and its weight is lessened, and the liquid crystal panel is used as a display portion of various kinds of information equipment and portable equipment, such as a personal computer, a video camera, and a digital camera.
Recently, a pocket-sized small portable information processing terminal device (mobile computer) which is superior to a note-sized personal computer in portability and is inexpensive, becomes popular, and an active matrix type liquid crystal panel is used as its display portion. In such an information processing terminal device, data can be inputted from the display portion in a touch-pen system. However, it is necessary to connect it with a peripheral equipment for reading a picture, such as a scanner or a digital camera, in order to input character/drawing information on a sheet or image information. Thus, the portability of the information processing terminal device is vitiated. Moreover, an economical burden is imposed on users.
The active matrix type liquid crystal display device is also used for a display portion of a TV meeting system, a TV telephone, a terminal for the Internet, and the like. Although such a system or terminal includes a camera (CCD camera) for taking a picture of a dialogist or a user, a display portion and a reading portion (sensor portion) are separately manufactured, and are made into a module. Thus, the manufacturing cost is high.